This invention refers to fluid actuated rodless cylinders and more particularly relates to a sealing device for pneumatic cylinders without rod of the type having a hollow body or barrel defining an elongated chamber in which a piston member reciprocates, said piston being connected to a power transmission element through a slot longitudinally extending on a wall of the cylinder.
Cylinders without rod have long been used to effect reciprocating movements or positioning of objects by using pressurized fluid, generally, compressed air, as power source. These rodless cylinders, See GB-A-2163499, EP-A-0147803, U.S. Pat. No. 2,745,382 and DE-C-846493, differently from traditional cylinders provided with a power transfer rod protruding from one or both ends, transfer rod protruding from one or both ends, usually have a longitudinally sliding carriage or power transmission element movable on the cylinder body; the power transmission element is directly connected to a piston member inside the barrel of the cylinder through a longitudinal slot of adequate width. A sealing element consisting of a flexible strip is located inside the cylinder chamber and is urged by the pressurized fluid against the inner surface of the chamber to cover the slot to form a seal. An analogous sealing strip may be provided on the outside of the cylinder body along the longitudinal slot to prevent the entrance of dust. The internal and external sealing strips go through longitudinal passage ways in the piston and carriage members, which are provided with adequate spreading means to spread apart and respectively to approach the strips to the body of the cylinder during the reciprocating movement of the piston.
According to GB-A-2163499 and EP-A-0147803 the sealing strip comprises a sealing portion for creating a seal against an inner side wall of the cylinder barrel, adjacent the longitudinal slot, and retaining portions adapted for engagement with the inner and of the outer surfaces of the barrel along said longitudinal slot. The use of retaining portions protruding inside the longitudinal slot of the cylinder do not permit the power transmission element connected to the reciprocating piston member, to be adequately guided during reciprocations movement along the cylinder resulting in difficulties to withstand to lateral reaction forces acting on said power transmission element. Furthermore, the use of retaining members protruding into the longitudinal slot does not prevent the pressurised fluid from excaping at the failure of the sealing portions of the strip. From DE-D-846493 it is also known a sealing device comprising a V-shaped sealing strip provided with longitudinal retaining members protruding into lateral grooves of the cylinder, having lateral surfaces parallelly arranged to radial surfaces of the longitudinal slot; according to this device the sealing action is therefore provided pressing the outer surface of the strip, between the retaining members, against the inner surface of the cylinder, near to said longitudinal slot. Owing to the thickness of the middle portion of the sealing strip, and consequently its reduced flexibility in a cross-wise direction, the sealing action may be reduced or compromised by wearing or any injuring of the sealing strip. Furthermore, in cylinders having long barrels, the long sealing strip may not be prevented from falling down, in absence of pressurised fluid into the chamber, when the longitudinal slot and the sealing strip are oriented upwardly or on a side.
An object of present invention is to provide a sealing device for rodless fluid actuated cylinders designed to avoid the disvantages of the sealing devices in rodless cylinders previously known.
In particular, a main object of the invention is to provide a sealing device for rodless cylinders allowing the sealing strip to be positively engaged with longitudinal grooves inside the barrel, in absence of pressurised fluid while maintaining the longitudinal slot completely free from the strip retaining means and providing guiding surface for the power transmission member on both sides of the slot.
A further object of the invention is to provide a rodless cylinder having a sealing device designed to improve and to maintain the sealing action by the retaining members, at the failure of the sealing strip, preventing the pressurised fluid to escape.